President Barack Obama on Tuesday will announce a long-awaited federal strategy to address climate change, a problem that this week he called "the global threat of our time."

"There’s no single step that can reverse the effects of climate change," he said Saturday in a video announcement. "But when it comes to the world we leave our children, we owe it to them to do what we can."

In his video message, Obama said the vision he'll lay out will include a national plan to reduce carbon pollution. It's expected to include regulating greenhouse gas emissions from existing power plants.

It also is expected to include what's known as mitigation -- addressing the impacts of climate change that many American communities are already experiencing, whether it's rising sea levels on the East Coast or melting sea ice in the Arctic. Obama is also expected to promise to lead global efforts to fight climate change.

The White House has been telegraphing for weeks that it would be announcing a plan this summer, and it is expected to have as its centerpiece rules that address greenhouse gas emissions from power plants. The administration, through the Environmental Protection Agency, already has drafted rules that curtail emissions at new power plants. What it hasn't done yet is come out with rules that apply to existing power plants.

That's likely to be controversial, since many of the dirtiest, carbon-intensive powered plants are fueled by coal, and regional energy interests are likely to object.

But courts have determined that carbon emissions are a pollutant under the Clean Air Act, and that the EPA has the authority to pursue regulation of them.

Obama in his second inaugural address pledged to respond to climate change. He cast it as a moral obligation and warned that failing to take action "would betray our children and future generations." It’s not just a responsibility to his fellow Americans, Obama said, but to "all posterity."

Environmental groups have been pressuring Obama to act on the promises laid out in that speech. This week, the Natural Resources Defense Council launched ads featuring actor Robert Redford calling on the president to act on the "courage of his convictions."

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